How to find the Windows version from the PowerShell command line?

How do I find which Windows version I'm using?

I'm using PowerShell 2.0 and tried:

PS C:\> ver
The term 'ver' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify tha
t the path is correct and try again.
At line:1 char:4
+ ver <<<<
+ CategoryInfo : ObjectNotFound: (ver:String) [], CommandNotFoundException
+ FullyQualifiedErrorId : CommandNotFoundException